mc9s08qg8 Freescale Semiconductor, Inc, mc9s08qg8 Datasheet - Page 138

• Manufacturer Part Number: mc9s08qg8
• Description: Hcs08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Analog-to-Digital Converter (S08ADC10V1)
There are some situations where external system activity causes radiated or conducted noise emissions or
excessive V
wait or stop3 or I/O activity cannot be halted, these recommended actions may reduce the effect of noise
on the accuracy:
9.6.2.4
The ADC quantizes the ideal straight-line transfer function into 1024 steps (in 10-bit mode). Each step
ideally has the same height (1 code) and width. The width is defined as the delta between the transition
points to one code and the next. The ideal code width for an N bit converter (in this case N can be 8 or 10),
defined as 1
There is an inherent quantization error due to the digitization of the result. For 8-bit or 10-bit conversions
the code will transition when the voltage is at the midpoint between the points where the straight line
transfer function is exactly represented by the actual transfer function. Therefore, the quantization error
will be ± 1/2
conversion is only 1/2
9.6.2.5
The ADC may also exhibit non-linearity of several forms. Every effort has been made to reduce these
errors but the system should be aware of them because they affect overall accuracy. These errors are:
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— For stop3 mode operation, select ADACK as the clock source. Operation in stop3 reduces V
There is no I/O switching, input or output, on the MCU during the conversion.
Place a 0.01 µF capacitor (C
improve noise issues but will affect sample rate based on the external analog source resistance).
Average the result by converting the analog input many times in succession and dividing the sum
of the results. Four samples are required to eliminate the effect of a 1
Reduce the effect of synchronous noise by operating off the asynchronous clock (ADACK) and
averaging. Noise that is synchronous to ADCK cannot be averaged out.
Zero-scale error (E
the actual code width of the first conversion and the ideal code width (1/2
conversion is $001, then the difference between the actual $001 code width and its ideal (1
used.
Full-scale error (E
the last conversion and the ideal code width (1.5
difference between the actual $3FE code width and its ideal (1
Differential non-linearity (DNL) — This error is defined as the worst-case difference between the
actual code width and the ideal code width for all conversions.
noise but increases effective conversion time due to stop recovery.
DD
LSB
LSB
Code Width and Quantization Error
Linearity Errors
noise is coupled into the ADC. In these situations, or when the MCU cannot be placed in
, is:
in 8- or 10-bit mode. As a consequence, however, the code width of the first ($000)
LSB
FS
and the code width of the last ($FF or $3FF) is 1.5
ZS
) — This error is defined as the difference between the actual code width of
) (sometimes called offset) — This error is defined as the difference between
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 1.01
1
AS
LSB
) on the selected input channel to V
= (V
REFH
- V
REFL
LSB
) / 2
). Note, if the last conversion is $3FE, then the
N
LSB
) is used.
REFL
LSB
LSB
or V
, one-time error.
.
LSB
Freescale Semiconductor
SSAD
). Note, if the first
(this will
Eqn. 9-2
LSB
) is
DD